There are known apparatuses and methods using light rays or beams for checking the dimensions or the presence, the arrangement and possible breakages of mechanical component parts, for example of tools in machine tools.
U.S. Pat. No. 3,912,925 discloses, for example, a drilling machine in which devices for checking the integrity of the tools employ transversal light beams which have limited thickness and are substantially coplanar with respect to the feed direction of the tools. The non-interruption of a light beam at a specific position of the tool is detected, and notifies an anomalous condition of the tool.
U.S. Pat. No. 3,749,500 shows different applications of optical gauges for checking dimensions (diameters of cylindrical pieces) or wear of tools (FIG. 17). Other checking apparatuses that employ a light beam and detect its interruption are known from other patent documents, such as publications No. FR-A-2343555, EP-A-0098930, EP-A-1050368 and DE-10337242.
In the optical and optoelectronic apparatuses, component parts such as lenses, mirrors, photodiodes, etc., are needed to be protected against dust and other foreign materials. This need is particularly pressing in optoelectronic apparatuses which operate in industrial environments, for example for checking dimensions of pieces with high standards of accuracy.
In the checking apparatuses using a light beam and operating in a workshop environment, the presence of dirt located at the emitter and/or the receiver affects the correct reception of the emitted light beam in a direct and hard way, and thus affects the correct operation of the apparatus. Such a problem is faced and partly solved in different ways. As disclosed in patent No. DE-A-10227242, there can be movable mechanical protections such as shutters that uncover the optical devices only during the time interval in which the checking is carried out. In such a way, in the course of the machining, the optical device is mechanically protected and the propagation conduit of the light beam can not be reached by chips and cooling. There can be also included cleaning nozzles blowing compressed air on the glasses of the casing that house the optical devices, as mentioned and shown for example in patent applications No. EP-A-0098930 and EP-A-1050368. The latter document also shows different solutions, wherein an optical device comprises a mechanical protection screen with a conduit for allowing the light beam in output (in case of the emitter) or in input (in case of the receiver) to pass through, and a pneumatic circuit blowing compressed air outwards from said casing through said conduit for preventing the dirt or other foreign material from penetrating from the conduit and reaching the optical device.
Documents no. U.S. Pat. No. 3,749,500 and DE-A 10337242 also comprise the implementation of pressurized units housing the optical devices.
According to the known solutions disclosed in the documents No. EP-A-1050368 and DE-A-10337242, the compressed air passes through the conduit of the light beam even—and especially—during the checking operations carried out by means of the apparatus. The turbulences in the compressed air stream can negatively affect the correct operation of the apparatus, causing unwanted and uncontrollable reflections and refractions of the light beam which is transmitted and/or received. For the purpose of overcoming, at least partly, such a problem the patent application No. EP-A-1050368 shows conduits being oblique with respect to the light beam direction, so as to minimize the negative influence of the compressed air stream on the correct propagation of the light beam. According to a different embodiment disclosed in the patent application No. DE-A-10337242, a porous “homogenizing” element located inside the protection casing filters the air so causing a laminar flow in the stream aimed to pass through the conduit. This enables to limit vortex and turbulences and thus the negative and uncontrollable effects on the light beam. The “homogenizing” element can be tubular-shaped and can be made of sintered material (metal, plastic, or other material), which is worked in such a way to obtain holes and slots having dimensions of some tens of micron.
Even thought the mentioned disadvantage is limited, both the solutions do not enable to substantially solve the problem: the negative influence on the light beam caused by the air stream, with a necessarily high flow, passing through the same conduit during the checking operations of the apparatus is not completely avoided.